Gas engine lubricating oil composition, and method for improving fuel consumption and/or for reducing abnormal combustion

ABSTRACT

A gas engine lubricating oil composition, comprising a lubricating base oil, an anti-wear agent which contains phosphorus as a constituent element and does not contain sulfur as a constituent element, an organomolybdenum friction modifier, a calcium salicylate detergent, and a magnesium salicylate detergent, wherein the ratio of a calcium element content in the composition to a magnesium element content in the composition is 1.50 to 1.80, and wherein the amount of sulfated ash measured in accordance with JIS K2272 is 0.6 mass % or less, is disclosed

TECHNICAL FIELD

The present invention relates to a gas engine lubricating oil composition, and a method for improving fuel consumption and/or for reducing abnormal combustion.

BACKGROUND

The gas engine cogeneration system is a system in which electric power is generated by a gas engine and exhaust heat is used as energy. In the gas engine used in such system, due to continuous high load operation, a gas engine lubricating oil gradually oxidizes and deteriorates and needs to be exchanged at regular intervals. In order to reduce the number of exchanges it is demanded that a gas engine lubricating oil have a long life.

In recent years a highly efficient gas engine cogeneration system has been urgently needed, and the downsizing of engines and fuel efficiency by a reduction in engine friction have been considered. However, the occurrence of abnormal combustion (pre-ignition) in an engine accompanied with high engine output is regarded as a problem. Therefore, a gas engine lubricating oil is demanded to suppress abnormal combustion in addition to having a long life.

A gas engine lubricating oil generally comprises a lubricating base oil and additives selected depending on demand properties as described above. Patent Literatures 1 to 5, for example, disclose a lubricating oil composition comprising a phosphorus additive, a metal detergent, etc. from the viewpoint of anti-wear characteristics, base number retention characteristics and high temperature detergency.

CITATION LIST Patent Literature

Patent Literature 1: JP 2002-294271

Patent Literature 2: JP 2003-277781

Patent Literature 3: JP 2003-277782

Patent Literature 4: JP 2003-277783

Patent Literature 5: JP 2006-124537

SUMMARY

However, conventional lubricating oil compositions also have room for further improvement particularly on the suppression of abnormal combustion. Therefore, a main object of the present invention is to provide a gas engine lubricating oil composition which has long life performance and fuel efficiency characteristics and moreover can suppress abnormal combustion.

In order to solve the above problems, the present invention provides lubricating oil compositions described in [1] to [4] below, a method for improving fuel consumption and/or for reducing abnormal combustion described in [5] below.

[1] A gas engine lubricating oil composition, comprising a lubricating base oil, an anti-wear agent which contains phosphorus as a constituent element and does not contain sulfur as a constituent element, an organomolybdenum friction modifier, a calcium salicylate detergent, and a magnesium salicylate detergent, wherein the ratio of a calcium element content in the composition to a magnesium element content in the composition is 1.50 to 1.80, and wherein the amount of sulfated ash measured in accordance with JIS K2272 is 0.6 mass % or less.

[2] The gas engine lubricating oil composition according to [1], wherein the ratio of the calcium salicylate detergent content in the composition, in terms of calcium element, to the magnesium salicylate detergent content in the composition, in terms of magnesium element, is 1.50 to 1.80.

[3] The gas engine lubricating oil composition according to [1] or [2], having a kinematic viscosity at 100° C. of 10 to 12 mm²/s.

[4] The gas engine lubricating oil composition according to any of [1] to [3], further comprising at least one selected from the group consisting of an antioxidant and an ashless dispersant.

[5] A method for improving fuel consumption and/or for reducing abnormal combustion, the method comprising a step of lubricating a gas engine using a gas engine lubricating oil composition, comprising a lubricating base oil, an anti-wear agent which contains phosphorus as a constituent element and does not contain sulfur as a constituent element, an organomolybdenum friction modifier, a calcium salicylate detergent, and a magnesium salicylate detergent, wherein the ratio of a calcium element content in the composition to a magnesium element content in the composition is 1.50 to 1.80, and wherein the amount of sulfated ash measured in accordance with JIS K2272 is 0.6 mass % or less.

According to the present invention, there is provided a gas engine lubricating oil composition, which has long life performance and fuel efficiency characteristics and moreover can suppress abnormal combustion. According to the present invention, there is also provided a method for improving fuel consumption and/or for reducing abnormal combustion, which provides lubricating a gas engine using a gas engine lubricating oil composition.

DETAILED DESCRIPTION

The embodiment of the present invention will now be described in detail. It should be noted, however, that the present invention is not limited to the following embodiment.

A gas engine lubricating oil composition in one embodiment comprises a lubricating base oil, an anti-wear agent which contains phosphorus as a constituent element and does not contain sulfur as a constituent element, an organomolybdenum friction modifier, a calcium salicylate detergent, and a magnesium salicylate detergent.

[Lubricating Base Oil]

As the lubricating base oil, lubricating base oils which are used in the normal lubricating oil field can be used. As the lubricating base oil, there is specifically a mineral base oil, a synthetic base oil or a mixture thereof.

Examples of mineral base oils include a kerosene distillate obtained by distilling paraffinic, naphthenic or aromatic crude oil; normal paraffin obtained from a kerosene distillate by e.g. extraction operation; a lubricating oil distillate obtained by distilling paraffinic, naphthenic or aromatic crude oil, or paraffinic mineral oil, naphthenic mineral oil, normal paraffinic base oil, isoparaffinic base oil, aromatic base oil and the like obtained by refining, raw materials, a wax such as slack wax obtained by a lubricating oil dewaxing process and/or a synthetic wax such as Fischer-Tropsch wax or GTL wax obtained by e.g. Gas-to-liquid (GTL) process, by one of refining treatments such as solvent deasphalting, solvent extraction, hydrocracking, hydroisomerization, solvent dewaxing, catalytic dewaxing, hydrotreating, sulfuric acid treatment and clay treatment, or suitably combining two or more refining treatments. These mineral base oils can be used individually or two or more mineral base oils can be used in combination at any ratio.

Examples of synthetic base oils include poly α-olefins or hydrides thereof; olefin oligomers such as a propylene oligomer, an isobutylene oligomer, a polybutene, a 1-octene oligomer, a 1-decene oligomer, an ethylene-propylene oligomer or hydrides thereof; alkylbenzenes; alkylnaphthalenes; diesters (such as ditridecyl glutarate, di-2-ethylhexyl adipate, di-2-ethylhexyl azelate, diisodecyl adipate, ditridecyl adipate, and di-2-ethylhexyl sebacate); polyol esters (such as trimethylolpropane caprylate, trimethylolpropane pelargonate, trimethylolpropane oleate, pentaerythritol 2-ethylhexanoate, and pentaerythritol pelargonate); polyoxyalkylene glycols, dialkyldiphenyl ethers, polyphenyl ethers and the like. These synthetic base oils can be used individually or two or more synthetic base oils can be used in combination at any ratio.

The kinematic viscosity at 100° C. of the lubricating base oil is not particularly restricted, and can be 6.0 mm²/s or more, 6.2 mm²/s or more or 6.3 mm²/s or more. When the kinematic viscosity at 100° C. is 6.0 mm²/s or more, there is a tendency that oil film formation and volatility of product are better, and moreover wear resistant performance can be improved and fuel consumption can be depressed. In addition, the kinematic viscosity at 100° C. of the lubricating base oil can be 7.0 mm²/s or less, 6.8 mm²/s or less, or 6.7 mm²/s or less. When the kinematic viscosity at 100° C. is 7.0 mm²/s or less, there is a tendency that a sufficient high-efficiency (fuel efficiency) effect is further obtained by adding a viscosity index improver.

The kinematic viscosity at 40° C. of the lubricating base oil is not particularly restricted, and can be 30 mm²/s or more, 32 mm²/s or more, or 35 mm²/s or more. When the kinematic viscosity at 40° C. is 30 mm²/s or more, there is a tendency that oil film formation and volatility of product are better, and moreover wear resistant performance can be improved and fuel consumption can be depressed. In addition, the kinematic viscosity at 40° C. of the lubricating base oil can be 45 mm²/s or less, 40 mm²/s or less, or 38 mm²/s or less. When the kinematic viscosity at 40° C. is 45 mm²/s or less, there is a tendency that a sufficient high-efficiency (fuel efficiency) effect is further obtained by adding a viscosity index improver.

The viscosity index of the lubricating base oil is not particularly restricted, and can be 100 or more, 110 or more, or 120 or more. When the viscosity index is within the above range, the viscosity stability to external temperature is secured, and thus there is a tendency that an oil film can be formed with stability even to changes in external temperature when used.

The kinematic viscosity at 40° C. and 100° C. and viscosity index in the description mean values measured in accordance with “Crude petroleum and petroleum products-Determination of kinematic viscosity and calculation of viscosity index from kinematic viscosity” in JIS K2283 respectively.

[Anti-Wear Agent]

The lubricating oil composition comprises an anti-wear agent which contains phosphorus as a constituent element and does not contain sulfur as a constituent element. The long life performance can be improved by using such anti-wear agent.

The anti-wear agents which meet the above conditions are not particularly restricted, and include for example phosphorous acid esters (phosphites), phosphoric acid esters (phosphates), amine salts thereof, metal salts thereof, derivatives thereof and the like. These anti-wear agents can be used individually or two or more anti-wear agents can be used in combination at any ratio.

Among these, the anti-wear agent can be a zinc dialkyl phosphate (ZP), i.e. a compound represented by the following general formula (A).

In the formula (A), R²¹ to R²⁴ each independently represent a C1-24 straight or branched alkyl group.

The anti-wear agent content (C(P)) can be 100 to 1000 ppm by mass, in terms of phosphorus element, based on the total amount of the composition. The C(P) can be also 100 ppm by mass or more, 200 ppm by mass or more, or 300 ppm by mass or more. When the C(P) is 100 ppm by mass or more, there is a tendency that more sufficient anti-wear performance can be obtained in the lubricating oil composition. The C(P) can be also 1000 ppm by mass or less, 800 ppm by mass or less, or 600 ppm by mass or less. When the C(P) is 1000 ppm by mass or less, there is a tendency that an increase in deposits accompanied with an increase in the amount of ash and the poisoning of a catalyst of an exhaust after-treatment system can be further suppressed in the lubricating oil composition.

The phosphorus element content in the anti-wear agent is analyzed in advance by e.g. ICP elemental analysis, and the above C(P) can be found from the product of the analytical value and charged amount.

[Friction Modifier]

The lubricating oil composition comprises an organomolybdenum friction modifier.

Examples of organomolybdenum friction modifiers include organomolybdenum compounds which contain sulfur as a constituent element, organomolybdenum compounds which do not contain sulfur as a constituent element, and the like.

Examples of organomolybdenum compounds which contain sulfur as a constituent element include sulfur-containing organomolybdenum compounds such as molybdenum dithiocarbamate (MoDTC) and molybdenum dithiophosphate, and complexes of a molybdenum compound (e.g. a molybdenum oxide such as molybdenum dioxide or molybdenum trioxide, molybdic acid such as orthomolybdic acid, paramolybdic acid or molybdenum (poly)sulfide, a metal salt of these molybdic acids, a molybdic acid salt such as ammonium salt, etc.), and a sulfur-containing organic compound (e.g. an alkyl (thio)xanthate, thiadiazole, mercaptothiadiazole, thiocarbonate, tetrahydrocarbylthiuram disulfide, bis(di(thio)hydrocarbyl dithiophosphonate)disulfide, an organic (poly)sulfide, a sulfurized ester, etc.) or other organic compounds, and the like. These organomolybdenum compounds can be used individually or two or more organomolybdenum compounds can be used in combination at any ratio.

Examples of organomolybdenum compounds which do not contain sulfur as a constituent element include molybdenum-amine complexes, molybdenum-succinimide complexes, molybdenum salts of organic acids, molybdenum salts of alcohols, and the like. These organomolybdenum compounds can be used individually or two or more organomolybdenum compounds can be used in combination at any ratio. The molybdenum compounds forming a molybdenum-amine complex include molybdenum compounds which do not contain sulfur such as molybdenum trioxide or hydrates thereof (MoO₃.nH₂O), molybdic acid (H₂MoO₄), molybdic acid alkali metal salts (M₂MoO₄: M represents an alkali metal), ammonium molybdate ((NH₄)₂MoO₄ or (NH₄)₆[Mo₇O₂₄].4H₂O), MoCl₅, MoOCl₄, MoO₂Cl₂, MoO₂Br₂ and Mo₂O₃Cl₆.

The friction modifier content (C(Mo)) can be 100 to 1000 ppm by mass in terms of molybdenum element based on the total amount of the composition. The C(Mo) can be also 100 ppm by mass or more, 120 ppm by mass or more, or 150 ppm by mass or more. When the C(Mo) is 100 ppm by mass or more, there is a tendency that more sufficient friction reducing performance can be obtained in the lubricating oil composition. The C(Mo) can be also 1000 ppm by mass or less, 500 ppm by mass or less, or 300 ppm by mass or less. When the C(Mo) is 1000 ppm by mass or less, there is a tendency that precipitate formation during product storage and an increase in deposits in an engine can be further suppressed in the lubricating oil composition.

The molybdenum element content in the friction modifier is analyzed in advance by e.g. ICP elemental analysis, and the above C(Mo) can be found from the product of the analytical value and charged amount.

[Metal Detergent]

The lubricating oil composition comprises a calcium salicylate detergent and a magnesium salicylate detergent.

The calcium salicylate detergent is a compound (calcium salicylate) represented by the following general formula (B).

In the formula (B), R^(b) represents a C14-28 straight or branched alkyl group. The number of carbons in R^(b) can be 14 to 20. nb represents the number of substituents of R^(b) and is 1 or 2. When nb is 2, R^(b) may be the same or different.

The method for producing calcium salicylate is not particularly restricted, and examples thereof include a method in which an alkyl salicylate is allowed to react with a metal base such as calcium oxide or calcium hydroxide, and a method in which an alkali metal salt such as a sodium salt or a potassium salt is once formed and then substituted with a calcium salt.

The calcium salicylate can be not only a neutral salt obtained by the above-described methods, but also a basic salt obtained by heating e.g. the neutral salt and an excess of alkali metal or alkaline-earth metal salt, an alkali metal or alkaline-earth metal base (a hydroxide, an oxide, etc. of an alkali metal or alkaline-earth metal) in the presence of water, and an overbased salt obtained by reacting a neutral salt with a base such as a hydroxide of an alkali metal or alkaline-earth metal in the presence of carbon dioxide, or boric acid or a boric acid salt.

The magnesium salicylate detergent is a compound (magnesium salicylate) represented by the following general formula (C).

In the formula (C), R^(c) represents a C14-28 straight or branched alkyl group. The number of carbons in R^(c) can be 14 to 25. nc represents the number of substitutes of R^(c) and is 1 or 2. When nc is 2, R^(c) may be the same or different.

The magnesium salicylate can be obtained by the same production method as for the above-described calcium salicylate.

The magnesium salicylate can be also a neutral salt, a basic salt or an overbased salt as in the case of the above-described calcium salicylate.

When the magnesium salicylate detergent content in the composition, in tennis of magnesium, is regarded as C(Mg) and the calcium salicylate detergent content in the composition, in terms of calcium element, is regarded as C(Ca), the ratio (C(Ca)/C(Mg)) of C(Ca) to C(Mg) can be 1.50 to 1.80. The C(Ca)/C(Mg) can be also 1.50 or more, 1.53 or more, or 1.55 or more. When the C(Ca)/C(Mg) is 1.50 or more, there is a tendency that the life of the lubricating oil composition is prolonged. The C(Ca)/C(Mg) can be also 1.80 or less, 1.70 or less, or 1.60 or less. When the C(Ca)/C(Mg) is 1.80 or less, there is a tendency that abnormal combustion of the lubricating oil composition is further suppressed.

The calcium element content in a calcium salicylate detergent is analyzed in advance by e.g. ICP elemental analysis, and the above C(Ca) can be found from the product of the analytical value and charged amount. Similarly, the magnesium element content in a magnesium salicylate detergent is analyzed in advance by e.g. 1CP elemental analysis, and the above C(Mg) can be found from the product of the analytical value and charged amount.

The total amount (C(Ca)+C(Mg)) of the magnesium salicylate detergent content (C(Mg)), in terms of magnesium element, and the calcium salicylate detergent content (C(Ca)), in terms of calcium element, can be 800 to 1500 ppm by mass. The C(Ca)+C(Mg) can be also 800 ppm by mass or more, 900 ppm by mass or more, or 1000 ppm by mass or more. When the C(Ca)+C(Mg) is 800 ppm by mass or more, there is a tendency that more sufficient detergency performance and long life performance can be obtained. In addition, the C(Ca)+C(Mg) can be also 1500 ppm by mass or less, 1400 ppm by mass or less, or 1300 ppm by mass or less. When the C(Ca)+C(Mg) is 1500 ppm by mass or less, there is a tendency that abnormal combustion can be further suppressed.

The lubricating oil composition may further comprise at least one selected from the group consisting of an antioxidant and an ashless dispersant.

The antioxidant is not particularly restricted, and antioxidants which are used in the normal lubricating oil field can be used. Examples of antioxidants include e.g. phenol and amine ashless antioxidants, e.g. copper and molybdenum metal antioxidants, and the like. Specific examples thereof include 4,4′-methylenebis(2,6-di-Cert-butylphenol), 4,4′-bis(2,6-di-tert-butylphenol) and the like as phenol ashless antioxidants, and phenyl-α-naphthylamine, alkylphenyl-α-naphthylamines, dialkyldiphenylamines, diphenylamine and the like as amine ashless antioxidants.

The antioxidant content can be 0.1 to 2.0 mass % based on the total amount of the composition.

The ashless dispersant is not particularly restricted, and ashless dispersants which are used in the normal lubricating oil field can be used. Examples of ashless dispersants include mono- or bis-succinimide having at least one straight or branched alkyl group or alkenyl group having 40 or more and 400 or less carbon atoms in a molecule, a benzylamine having at least one alkyl group or alkenyl group having 40 or more and 400 or less carbon atoms in a molecule, a polyamine having at least one alkyl group or alkenyl group having 40 or more and 400 or less carbon atoms in a molecule, denaturation products thereof by boron compounds, carboxylic acid, phosphoric acid, etc. and the like.

The ashless dispersant content can be 0.1 to 10 mass % based on the total amount of the composition.

The lubricating oil composition can further comprise any lubricating oil additive which is generally used depending on the object thereof. Examples of such additives include a pour point depressant, a corrosion inhibitor, a rust inhibitor, a demulsifying agent, a metal deactivator, an anti-foamer and the like.

Examples of pour point depressants include a polymethacrylate polymer which matches a lubricating base oil used, and the like.

Examples of corrosion inhibitors include benzotriazole, tolyltriazole, thiadiazole, imidazole compounds, and the like.

Examples of rust inhibitors include petroleum sulfonates, alkylbenzene sulfonates, dinonylnaphthalene sulfonates, alkenyl succinic acid esters, polyhydric alcohol esters, and the like.

Examples of demulsifying agents include non-ionic polyalkylene glycol surface active agents such as polyoxyethylene alkyl ethers, polyoxyethylene alkylphenyl ethers and polyoxyethylene alkylnaphthyl ethers, and the like.

Examples of metal deactivators include imidazoline, pyrimidine, azole derivatives, and the like.

Examples of anti-foamers include silicone oils with a kinematic viscosity at 25° C. of 100 to 1000000 mm²/s which may have an alkyl halide group, alkenyl succinic acid derivatives, esters of an aliphatic polyhydroxy alcohol and a long chain fatty acid, esters of methyl salicylate and o-hydroxybenzyl alcohol, and the like.

When using other lubricating oil additives, each content can be 0.01 to 20 mass % based on the total amount of the composition.

The phosphorus element content in the lubricating oil composition can be 100 to 1000 ppm by mass based on the total amount of the composition. The phosphorus element content in the lubricating oil composition is mainly derived from phosphorous element in the above-described anti-wear agent which contains phosphorus as a constituent element and does not contain sulfur as a constituent element. The phosphorus element content in the lubricating oil composition can be also 100 ppm by mass or more, 200 ppm by mass or more, or 300 ppm by mass or more. When the phosphorus element content in the lubricating oil composition is 100 ppm by mass or more, there is a tendency that more sufficient anti-wear performance can be obtained. The phosphorus element content in the lubricating oil composition can be also 1000 ppm by mass or less, 800 ppm by mass or less, or 600 ppm by mass or less. When the phosphorus element content in the lubricating oil composition is 1000 ppm by mass or less, there is a tendency that an increase in deposits accompanied with an increase in the amount of ash and the poisoning of a catalyst of an exhaust after-treatment system can be further suppressed.

The phosphorus element content in the lubricating oil composition can be directly found by e.g. ICP elemental analysis of the lubricating oil composition. In addition, the phosphorus element content in an additive containing phosphorus element is analyzed in advance by e.g. ICP elemental analysis, and the phosphorus element content in the lubricating oil composition can be also found from the product of the analytical value and charged amount.

The molybdenum element content in the lubricating oil composition can be 100 to 1000 ppm by mass based on the total amount of the composition. The molybdenum element content in the lubricating oil composition is mainly derived from molybdenum element in the above-described organomolybdenum friction modifier. The molybdenum element content in the lubricating oil composition can be also 100 ppm by mass or more, 120 ppm by mass or more, or 150 ppm by mass or more. When the molybdenum element content in the lubricating oil composition is 100 ppm by mass or more, there is a tendency that more sufficient friction reducing performance can be obtained. The molybdenum element content in the lubricating oil composition can be also 1000 ppm by mass or less, 500 ppm by mass or less, or 300 ppm by mass or less. When the molybdenum element content in the lubricating oil composition is 1000 ppm by mass or less, there is a tendency that precipitate formation during product storage and an increase in deposits in an engine can be further suppressed.

The molybdenum element content in the lubricating oil composition can be directly found by e.g. ICP elemental analysis of the lubricating oil composition. In addition, the molybdenum element content in an additive containing molybdenum element is analyzed in advance by e.g. ICP elemental analysis, and the molybdenum element content in the lubricating oil composition can be also found from the product of the analytical value and charged amount.

The ratio of the calcium element content to the magnesium element content in the lubricating oil composition (calcium element content/magnesium element content) is 1.50 to 1.80. The calcium element and magnesium element in the lubricating oil composition are mainly derived from calcium element in the above-described calcium salicylate detergent and magnesium element in the magnesium salicylate detergent, respectively. The ratio of the calcium element content to the magnesium element content can be also 1.50 or more, 1.53 or more, or 1.55 or more. When the ratio of the calcium element content to the magnesium element content is 1.50 or more, there is a tendency that the life of the lubricating oil composition is prolonged. The ratio of the calcium element content to the magnesium element content can be also 1.80 or less, 1.70 or less, or 1.60 or less. When the ratio of the calcium element content to the magnesium element content is 1.80 or less, there is a tendency that abnormal combustion of the lubricating oil composition is suppressed.

The calcium element content and magnesium element content in the lubricating oil composition can be directly found by e.g. ICP elemental analysis of the lubricating oil composition. Each element content in an additive containing each element is analyzed in advance by e.g. ICP elemental analysis, and each element content in the lubricating oil composition can be also found from the product of the analytical value and charged amount.

The total amount of the magnesium element content and the calcium element content in the lubricating oil composition can be 800 to 1500 ppm by mass. The total amount of the magnesium element content and the calcium element content can be also 800 ppm by mass or more, 900 ppm by mass or more, or 1000 ppm by mass or more. When the total amount of the magnesium element content and the calcium element content is 800 ppm by mass or more, there is a tendency that more sufficient detergency performance and life performance can be obtained. The total amount of the magnesium element content and the calcium element content can be also 1500 ppm by mass or less, 1400 ppm by mass or less, or 1300 ppm by mass or less. When the total amount of the magnesium element content and the calcium element content is 1500 ppm by mass or less, there is a tendency that abnormal combustion can be further suppressed.

The kinematic viscosity at 100° C. of the lubricating oil composition can be 10 to 12 mm²/s. The kinematic viscosity at 100° C. can be also 10 to 11.5 mm²/s or 10 to 11 mm²/s. When the kinematic viscosity at 100° C. is 10 mm²/s or more, there is a tendency that a better oil film can be obtained in the practical use temperature range. When the kinematic viscosity at 100° C. is 12 mm²/s or less, there is a tendency that a more sufficient high-efficiency (fuel efficiency) effect can be obtained.

The kinematic viscosity at 40° C. of the lubricating oil composition is not particularly restricted, and can be 50 mm²/s or more, 55 mm²/s or more, or 60 mm²/s or more. When the kinematic viscosity at 40° C. of the lubricating oil composition is 50 mm²/s or more, there is a tendency that a better oil film can be obtained in the practical use temperature range. In addition, the kinematic viscosity at 40° C. of the lubricating oil composition can be 70 mm²/s or less, 65 mm²/s or less, or 63 mm²/s or less. When the kinematic viscosity at 40° C. of the lubricating oil composition is 70 mm²/s or less, there is a tendency that a more sufficient fuel efficiency effect can be obtained.

The viscosity index of the lubricating oil composition is not particularly restricted, and can be 100 or more, 110 or more, or 120 or more. When the viscosity index is within the above range, the viscosity stability to external temperature is secured, and thus there is a tendency that an oil film can be formed with stability even to changes in external temperature when used.

The base number by the hydrochloric acid method of the lubricating oil composition is not particularly restricted, and can be 3.0 to 5.0 mg KOH/g. The base number can be also 3.5 to 5.0 mg KOH/g or 4.0 to 5.0 mg KOH/g. When the base number is 3.0 mg KOH/g or more, there is a tendency that more sufficient long life performance can be obtained. When the base number is 5.0 mg KOH/g or less, there is a tendency that metal components in the lubricating oil composition are within a suitable range, and abnormal combustion can be further suppressed. It should be noted that the base number by the hydrochloric acid method means a value measured in accordance with HS K2501.

The amount of sulfated ash in the lubricating oil composition is 0.6 mass % or less. When the amount of sulfated ash is 0.6 mass % or less, abnormal wear due to ash deposition on pistons and abnormal combustion can be suppressed. The amount of sulfated ash means a value measured in accordance with JIS K2272.

According to the gas engine lubricating oil composition of the present embodiment, long life performance and fuel efficiency characteristics are good, and moreover abnormal combustion can be suppressed. Therefore, it is possible to provide a method for improving fuel consumption and/or for reducing abnormal combustion, which provides lubricating a gas engine using such lubricating oil composition.

EXAMPLES

The present invention will now be described in more detail by way examples thereof. It should be noted, however, that the present invention is not limited to these examples.

Preparation of Lubricating Oil Compositions Examples 1 and 2 and Comparative Examples 1 to 4

As shown in Table 1, lubricating oil compositions in Examples 1 and 2 and Comparative Examples 1 to 4 each were prepared. It should be noted that when preparing a lubricating oil composition, the viscosity index improver content was mainly adjusted so that the kinematic viscosity at 100° C. would be in a range of 10.2 to 10.4 mm²/s. The obtained lubricating oil compositions were subjected to tests.

The details of each component shown in Table 1 are as follows.

<Lubricating Base Oil>

Base oil A-1: hydrotreated mineral oil (Gp III+) (YUBASE-6, 40° C. kinematic viscosity: 36.1 mm²/s, 100° C. kinematic viscosity: 6.42 mm²/s, viscosity index: 131)

<Lubricating Oil Additives>

Anti-wear agent B-1: zinc dialkyl phosphate (ZP) (manufactured by Johoku Chemical Co., Ltd. product name: DBP-Zn-50L, alkyl group: butyl group, phosphorus element content: 6.9 mass %)

Anti-wear agent b-1: zinc dialkyldithiophosphate (ZDTP) (manufactured by Chevron Oronite, OLOA 269RJ, alkyl group: n-octyl group, phosphorus element content: 7.1 mass %)

Friction modifier C-1: molybdic acid dialkylamine salt (manufactured by ADEKA CORPORATION, SAKURA-LUBE 710, alkyl group: tridecanyl group, molybdenum element content: 10 mass %)

Metal detergent D-1: overbased calcium salicylate (manufactured by OSCA CHEMICAL CORPORATION, product name: OSCA 463, calcium element content: 6.5 mass %) Metal detergent D-2: neutral calcium salicylate (manufactured by OSCA CHEMICAL CORPORATION, product name: LB 622, calcium element content: 1.8 mass %)

Metal detergent D-3: magnesium salicylate (manufactured by OSCA CHEMICAL CORPORATION, magnesium element content: 2.1 mass %)

Ashless dispersant E-1: polyalkenyl succinimide (manufactured by Chevron Oronite, OLOA 5096, weight average molecular weight: 4000 to 6000, nitrogen element content: 1.5 mass %, boron element content: 0.5 mass %)

Antioxidant F-1: amine antioxidant (manufactured by BASF, product name: IRGANOX L57, monobutylphenyl monooctylphenyl amine, nitrogen element content: 4.5 mass %) 0.3 mass % (based on the total amount of composition) and phenol antioxidant (manufactured by BASF, product name: IRGANOX L135, hindered phenol, nitrogen element content: 4.5 mass %) 0.3 mass % (based on the total amount of composition)

Viscosity index improver G-1: a mixed polymer of a polymethacrylate and an olefin copolymer (manufactured by Evonik Degussa Japan Co., Ltd., product name: VISCOPLEX 2-602)

Each element content in each lubricating oil additive was found by ICP elemental analysis. In addition, in Table 1, each lubricating oil additive content in terms of each element (value converted to element) based on the composition and each element content in the composition were found from the product of each element content in each lubricating oil additive and charged amount.

(1) Viscosity Properties

The kinematic viscosity at 40° C. and 100° C. and viscosity index of each lubricating oil composition were measured in accordance with “Crude petroleum and petroleum products-Determination of kinematic viscosity and calculation of viscosity index from kinematic viscosity” in JIS K2283.

(2) Acid Number and Base Number

The acid number and base number by the hydrochloric acid method of each lubricating oil composition were measured in accordance with JIS K2501.

(3) Amount of Sulfated Ash

The amount of sulfated ash in each lubricating oil composition was measured in accordance with JIS K2272.

(4) NOx injection test (long life performance)

The NOx injection test was carried out for each lubricating oil composition. The test conditions are described below. After the test, the base number by the hydrochloric acid method of each lubricating oil composition was measured in accordance with HS K2501, and the ratio of the base number after the test to the base number before the test ([base number after test]/[base number before test]) was calculated as the “base number retention rate after NOx test”. In the test, a larger value (e.g. 10% or more) further maintains the base number of the lubricating oil composition, which means a long life.

<Test Conditions>

Mixed gas: a mixed gas of oxygen (85%), NO₂ (1000 ppm) and nitrogen (rest)

Test temperature: 140° C.

Test time: 96 hours

(5) SRV test (fuel efficiency characteristics)

The SRV test was carried out for each lubricating oil composition using a cylinder-on-disc reciprocating friction tester to measure friction coefficient. The test conditions are described below. In the test, a smaller value (e.g. 0.15 or less) has better friction properties, which means better fuel efficiency characteristics.

<Test conditions>

Load: 170 N

Frequency: 50 Hz

Test temperature: 80° C.

Test time: 30 minutes

(6) High pressure DSC (differential scanning calorimetry) test (oxidation stability)

The change in heat quantity was measured for each lubricating oil composition using a high pressure differential scanning calorimeter (high pressure DSC) and evaluated using the onset temperature (onset) of the DSC chart as the oxidation onset temperature. The test conditions are described below. In the test, a larger value (e.g. 270° C. or higher) means that oxidation (i.e. autoignition (combustion) phenomenon) is further suppressed.

<Test Conditions>

Measurement atmosphere: under air atmosphere

Pressure: 1.0 MPa (10 atm)

Temperature increasing conditions: maintaining 50° C. for 5 minutes and then increasing the temperature to 500° C. at 10° C./min

TABLE 1 Comp. Comp. Comp. Comp. Exam. 1 Exam. 2 Exam. 1 Exam. 2 Exam. 3 Exam. 4 Base oil (Based on total amount of composition) Base oil A-1 balance balance balance balance balance balance Additives (Based on total amount of composition) Anti-wear agent B-1 mass % 0.7 0.7 0 0.7 0.7 0.7 Anti-wear agent b-1 mass % 0 0 0.7 0 0 0 Value converted to P mass ppm 470 470 500 470 470 470 element (C(P)) Friction modifier C-1 mass % 0.15 0.15 0 0 0.15 0.15 Value converted to Mo mass ppm 150 150 0 0 150 150 element (C(Mo)) Metal detergent D-1 mass % 1.1 1.1 1.7 1.1 1.0 1.1 Metal detergent D-2 mass % 0 0.3 0 3.3 0 0.6 Metal detergent D-3 mass % 2.1 2.0 0 0 2.4 1.9 Value converted to Ca mass ppm 710 770 1100 1300 700 820 element (C(Ca)) Value converted to Mg mass ppm 450 430 0 0 500 410 element (C(Mg)) C(Ca) + C(Mg) mass ppm 1160 1200 1100 1300 1200 1230 C(Ca)/C(Mg) 1.58 1.79 — — 1.40 2.00 Ashless dispersant E-1 mass % 4.5 4.5 4.5 4.5 4.5 4.5 Antioxidant F-1 mass % 0.6 0.6 1.0 0.6 0.6 0.6 Viscosity index mass % 2.0 2.0 2.0 2.0 2.0 2.0 improver G-1 Properties of lubricating oil composition (Based on total amount of composition) P content mass ppm 470 470 500 470 470 470 Mo content mass ppm 150 150 0 0 150 150 Ca content mass ppm 710 770 1100 1300 700 820 Mg content mass ppm 450 430 0 0 500 410 Ca content + Mg mass ppm 1160 1200 1100 1300 1200 1230 content Ca content/Mg content 1.58 1.79 — — 1.40 2.00 Kinematic viscosity  40° C. mm²/s 61.0 61.3 60.8 61.7 61.2 62.0 100° C. mm²/s 10.3 10.3 10.2 10.3 10.3 10.4 Viscosity index 158 157 156 155 157 154 Acid number mg 2.4 2.3 1.8 1.7 2.2 2.5 KOH/g Base number mg 4.5 4.5 3.9 4.3 4.5 4.6 KOH/g Sulfated ash amount mass % 0.58 0.58 0.50 0.54 0.58 0.58 Base number retention % 15.5 16.2 0.5 23.8 5.5 18.0 rate after NOx test SRV test metal friction 0.14 0.13 0.20 0.22 0.16 0.15 coefficient High pressure DSC ° C. 285 276 254 257 291 265 oxidation onset temperature

In the lubricating oil compositions in Examples 1 and 2, high levels of long life performance, fuel efficiency characteristics and oxidation stability were obtained. Contrarily, in the lubricating oil composition in Comparative Example 1 which uses an anti-wear agent containing sulfur as a constituent element and does not contain an organomolybdenum friction modifier and a magnesium salicylate detergent, long life performance, fuel efficiency characteristics and oxidation stability all were insufficient as compared to those of the lubricating oil compositions in Examples 1 and 2. In addition, in the lubricating oil composition in Comparative Example 2 which does not contain an organomolybdenum friction modifier and a magnesium salicylate detergent, long life performance were good but fuel efficiency characteristics and oxidation stability were insufficient as compared to those of the lubricating oil compositions in Examples 1 and 2. On the other hand, it turned out that in the lubricating oil compositions in Comparative Examples 3 and 4 in which the ratio of the calcium element content to the magnesium element content in the composition is not within a specific range, long life performance and oxidation stability contradicted each other and high levels of these properties could not be obtained. These results verified that the gas engine lubricating oil composition of the present invention had long life performance and fuel efficiency characteristics, and moreover can suppress abnormal combustion. 

What is claimed is:
 1. A gas engine lubricating oil composition comprising: a lubricating base oil; an anti-wear agent which contains phosphorus as a constituent element and does not contain sulfur as a constituent element; an organomolybdenum friction modifier; a calcium salicylate detergent; and a magnesium salicylate detergent; wherein the ratio of a calcium element content in the composition to a magnesium element content in the composition is 1.50 to 1.80, and wherein the amount of sulfated ash measured in accordance with JIS K2272 is 0.6 mass % or less.
 2. The gas engine lubricating oil composition according to claim 1, wherein the ratio of the calcium salicylate detergent content in the composition, in terms of calcium element, to the magnesium salicylate detergent content in the composition, in terms of magnesium element, is 1.50 to 1.80.
 3. The gas engine lubricating oil composition according to claim 1, having a kinematic viscosity at 100° C. of 10 to 12 mm²/s.
 4. The gas engine lubricating oil composition according to claim 1, further comprising at least one selected from the group consisting of an antioxidant and an ashless dispersant.
 5. A method for improving fuel consumption and/or for reducing abnormal combustion, the method comprising a step of lubricating a gas engine using a gas engine lubricating oil composition comprising: a lubricating base oil; an anti-wear agent which contains phosphorus as a constituent element and does not contain sulfur as a constituent element; an organomolybdenum friction modifier; a calcium salicylate detergent; and a magnesium salicylate detergent; wherein the ratio of a calcium element content in the composition to a magnesium element content in the composition is 1.50 to 1.80, and wherein the amount of sulfated ash measured in accordance with JIS K2272 is 0.6 mass % or less. 